Internal Combustion Engine Having Exhaust Gas Recirculation Loop With Catalyzed Heat Exchanger for Steam Reformation

ABSTRACT

A method of providing recirculated exhaust to an internal combustion engine. The engine has an EGR (exhaust gas recirculation loop) which may be a high pressure loop, a low pressure loop, or a dedicated cylinder loop. A catalyzed heat exchanger on the EGR loop has a steam reformation catalyst and a heat exchanger. The heat exchanger uses hot exhaust gas from the main exhaust line to heat the catalyst. A methane fuel source adds methane to the recirculated exhaust stream before it enters the catalyst, and the catalytic reaction increases the amount of hydrogen and carbon monoxide in the recirculated exhaust.

TECHNICAL FIELD OF THE INVENTION

This invention relates to internal combustion engines with exhaust gasrecirculation, and more particularly to improving the composition of therecirculated exhaust.

BACKGROUND OF THE INVENTION

For many internal combustion engines, their engine control strategy hasthree important parameters: spark timing (or fuel injection timing in adiesel engine), the exhaust gas recirculation (EGR) rate and theair/fuel ratio (AFR).

To implement EGR, a fraction of the exhaust gas is recycled from theexhaust system back to the intake system. The recirculated exhaust gasis mixed with the fresh fuel-air mixture before entering the cylinders.

EGR can be implemented in internal and external configurations. Externalconfigurations can be implemented as either a high pressure or lowpressure loop, depending on whether the recirculated exhaust isintroduced to the intake post compressor (high pressure loop) orpre-compressor (low pressure loop).

EGR has a long history of use in both diesel and spark-ignited enginesfor reduction of NOx emissions. It affects combustion in several ways.The combustion is cooled by the presence of exhaust gas, that is, therecirculated exhaust gas absorbs heat. The reduction of peak gastemperatures in the combustion chamber reduces the production of NOx.

One approach to implementing EGR is with one or more dedicated EGRcylinders. In a “dedicated EGR” engine, the one or more dedicatedcylinders are used to generate exhaust gas, all of which is dedicated torecirculation. With dedicated EGR, the quality of the recirculatedexhaust can be improved with in-cylinder reforming of gasoline tohydrogen (H₂) and carbon monoxide (CO). Subsequent combustion of thisexhaust, mixed with the fresh air intake to produce the intake charge,is thereby enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 illustrates an example of an internal combustion engine having adedicated EGR cylinder and a steam reformation catalyst in accordancewith the invention.

FIG. 2 illustrates a catalyzed heat exchanger in accordance with theinvention.

FIG. 3 illustrates an example of an internal combustion engine having ahigh pressure loop for EGR and a steam reformation catalyst inaccordance with the invention.

FIG. 4 illustrates an example of an internal combustion engine having alow pressure loop for EGR and a steam reformation catalyst in accordancewith the invention.

FIG. 5 illustrates how conversion of methane improves as temperatureincreases, for membrane and packed bed reactors.

FIGS. 6 and 7 illustrate expected H₂ and CO percentages, respectively,in the exhaust stream as a result of use of the catalyzed heatexchanger.

DETAILED DESCRIPTION OF THE INVENTION

The following description is directed to systems and methods forimproving the operation of an internal combustion engine having exhaustgas recirculation (EGR). A steam reforming catalyst with a built-in heatexchanger (referred to herein as a “catalyzed heat exchanger”) isinstalled in the EGR loop for the purpose of increasing the H2 and COcontent of the recirculated exhaust.

The catalyzed heat exchanger may be used with either a high pressureloop or low pressure loop EGR system. It may also be used with adedicated EGR system.

Catalyzed Heat Exchanger with Dedicated EGR

FIG. 1 illustrates an internal combustion engine 100 having fourcylinders 101. One of the cylinders is a dedicated EGR cylinder,identified as cylinder 101 d. Cylinder 101 d has an exhaust port thatopens only to an EGR loop 110. The other cylinders 101 produce exhaustthat exits the engine via the main exhaust line 119 and one or moreexhaust aftertreatment devices 120.

In the example of this description, engine 100 is spark-ignited, witheach cylinder 101 having an associated spark plug, and its “normal”air-fuel ratio (that of the cylinders 101 other than the dedicated EGRcylinder 101 d) is stoichiometric. Engine 100 may use various types offuels, such as gasoline, and the invention described herein isparticularly useful with natural gas fueled engines.

A feature of dedicated EGR is that the composition of the dedicated EGRexhaust gas may be controlled to be different from that of the exhaustof the non-dedicated cylinders. For example, the dedicated EGR cylinder101 d may be operated rich of stoichiometric to provide EGR thatimproves combustion on all cylinders. Thus, in a dedicated EGR engine,the dedicated and non dedicated cylinders may receive different amountsof fuel. This is in contrast to a conventional engine, in which thecylinders are typically fueled such that all cylinders receive the sameamount of fuel.

If a dedicated EGR cylinder is run rich of stoichiometric A/F ratio, asignificant amount of hydrogen (H₂) and carbon monoxide (CO) may beformed in the exhaust gas of the dedicated EGR cylinder. The benefits ofH₂ (for both increased knock and EGR tolerance) are greater than thebenefits of CO. Thus, it is desired to produce more H₂ than CO.

The dedicated EGR cylinder 101 d has all of its exhaust recirculatedback to the intake manifold 102. The exhaust of the other threecylinders 101 (referred to herein as the “main” or “non dedicated”cylinders) is directed to the main exhaust line 119 via an exhaustmanifold 103.

Engine 100 is equipped with a turbocharger, comprising a compressor 104a and a turbine 104 b. Although not explicitly shown, all cylinders 101have some sort of fuel delivery system for introducing fuel into thecylinders. This fuel delivery system can be fumigated, port injected, ordirect injected.

The EGR loop 110 joins the intake line downstream the compressor 104 a.A mixer 105 mixes the EGR and fresh air, and a cooler 106 reduces thetemperature of the intake charge. A throttle 107 controls the amount ofintake (fresh air and EGR) into the intake manifold 102. Various means,such as variable valve timing, valves, etc. (not shown), may be used tocontrol EGR flow.

The “EGR fraction” in the example of FIG. 1 is 25%, with one of fourcylinders 101 being a dedicated EGR cylinder. In other embodiments,there may be a different number of engine cylinders, and/or there may bemore than one dedicated EGR cylinder. In general, in a dedicated EGRengine configuration, the exhaust of a sub-group of cylinders is routedback to the intake of all the cylinders, thereby providing EGR for allcylinders.

After entering the cylinders 101, the fresh-air/EGR mixture is ignitedand combusts. After combustion, exhaust gas from each main cylinder 101flows through its exhaust port and into exhaust manifold 103. From theexhaust manifold 103, exhaust gas then flows through turbine 104 b,which drives compressor 104 a.

After turbine 104 b, exhaust gas flows to an exhaust aftertreatmentdevice 120 via the main exhaust line 119, to be treated before exitingto the atmosphere. Because only stoichiometric exhaust leaves theengine, the exhaust aftertreatment device 120 may be a three waycatalyst.

To control the air-fuel ratio, exhaust gas may be sampled by an exhaustgas oxygen (EGO) sensor. Both the main exhaust line 119 and the EGR loop110 may have a sensor (identified as 166 a and 166 b).

An EGR control unit (not shown) has appropriate hardware (processing andmemory devices) and programming for performing the methods describedherein. In addition, the control unit may perform other tasks, such asoverall EGR control, and may be integrated with a comprehensive enginecontrol unit.

A catalyzed heat exchanger (reactor) 180 is catalyzed to act as asteam-methane reformation catalyst, and is installed in-line on the EGRloop 110 to process the EGR exhaust. As explained below, heat exchanger180 uses exhaust from the main exhaust line 119 to raise the temperatureof the EGR exhaust.

A fuel injector 185 injects a methane source, such as natural gas orother hydrocarbon fuel, into the EGR stream upstream of catalyzed heatexchanger 180. In theory, any hydrocarbon fuel may be steam reformed.Specific examples are gasoline, diesel, methane, propane, and ethanol.

Fuel injector 185 is located downstream of the EGR take-off point fromdedicated EGR cylinder 101 d, and upstream of catalyzed heat exchanger180.

If engine 100 is fueled by natural gas, the methane source may be fromthe same fuel reservoir as used for the engine. In engines fueled withfuels other than natural gas, the methane source may be stored in anon-board reservoir (not shown) separate from that of the engine fuel.

Steam reforming of natural gas, sometimes referred to as steam methanereforming, is conventionally used commercially to produce bulk hydrogen.At high temperatures (500-1100° C.) and in the presence of a metal-basedcatalyst, steam reacts with methane (CH₄) to yield carbon monoxide (CO)and hydrogen (H₂). Steam reformation catalysts are typically formulatedwith nickel as the active metal, although other active components may beutilized.

The steam reformation reaction is endothermic, meaning energy isconsumed during the reaction. Heat must be supplied to the process forthe reaction to proceed. The lower heating value (or energy content) ofthe formed H₂ and CO mixture is greater than the lower heating value ofthe consumed CH₄. This allows for conversion of thermal energy tochemical energy in the form of H₂ and CO, as shown in the followingequation.

CH₄ (g)+H₂O (v)

CO+3H₂

As stated above, for purposes of recirculated exhaust, the benefits ofH₂ are greater than the benefits of CO. Therefore, it would be desiredfor catalyzed heat exchanger 180 to produce more H₂ than CO. Therelative production of H₂ and CO is pre-determined by the H:C ratio ofthe fuel used in the reforming process. Also, more H₂ and CO can begenerated using the steam reforming reaction if more thermal energy isavailable to drive the reactor.

To this end, catalyzed heat exchanger 180 is configured to transferthermal energy from the main exhaust stream to the EGR stream. In otherwords, catalyzer heat exchanger 180 is a combined catalyst/heatexchanger system. For the four-cylinder dedicated EGR engine of FIG. 1,catalyzed heat exchanger 180 has the potential to increase the thermalenergy of the EGR stream by up to a factor of three.

In one embodiment, catalyzed heat exchanger 180 comprises a hightemperature heat exchanger, which is coated with a catalyst material forthe steam reforming reaction. The main exhaust stream from main exhaustline 119 is used to keep the surface of the catalyst material at thesame temperature as the main exhaust stream. The surface temperature ofthe catalyst controls the chemical reaction rates, with the exhaust fromexhaust manifold 103 maintaining a constant catalyst surface temperatureleading to a high yield of H₂ and CO.

FIG. 2 is a cross-sectional view of an example of a catalyzed steamreformer 180. A housing 241 contains both a heat exchanger 243 and acatalyzed reactor 245. In the example of FIG. 2, exhaust from the mainexhaust line 119 enters an outer heat exchanger jacket 241 andcirculates around the surface of catalyst reactor 245. The heatexchanger jacket 241 transfers thermal energy from the main exhauststream to the EGR stream as thermal energy is converted in the EGRstream via the steam reforming reaction. This heat exchange maintainshigh catalyst surface temperature in the EGR stream as the EGR streamflows through the catalyzed reactor 245 and during the steam reformingreaction.

Catalyst 245 may be implemented with catalyzed pellets, honeycombsurfaces, or any other configuration used for catalytically treatingexhaust gas. Catalyst 245 may be a membrane reactor or packed-bedreactor, as discussed below in connection with FIG. 5.

As stated above, various catalytic materials may be used to coat thecatalyst surfaces or to coat the surface of the heat exchanger, forpurposes of the steam reformation reaction. Specific examples ofcatalyst materials are nickel, platinum, palladium, and rhodium.Catalyst supports can include cerium oxide, aluminum oxide, and siliconoxide.

Many other configurations for circulating exhaust from the main exhaustline 119 within catalyzed heat exchanger 180 are possible. Amultiplicity of straight tubes or U-shaped tubes or coils could be used.These various configurations could be used to heat the internal portionsof reactor 245 and not simply its outer surface. As stated above, thecatalyst material could be used as a coating on the heat exchangertubing.

Referring again to FIG. 1, the exhaust from the main cylinders istreated with a three-way catalyst (TWC) or other exhaust aftertreatmentdevice 120 installed on the main exhaust line 119. The placement of thecatalyzed heat exchanger 180 may be downstream the TWC 120, such as whena significant exotherm is generated across the TWC. In other embodimentsthe catalyzed heat exchanger may be positioned upstream of the TWC,close to the engine so that the EGR gas temperature is maintained ashigh as possible. In other words, the placement of the catalyzed heatexchanger 180 may depend on the design of a particular engine.

Catalyzed Heat Exchanger with HPL EGR

FIG. 3 illustrates an engine 300 having a high pressure EGR loop, inwhich all cylinders 301 contribute to the EGR flow. In other words,engine 300 does not use dedicated EGR. The “take-off” point for the EGRloop 310 is from the exhaust manifold 303. In other respects, engine 300is similar to engine 200.

Engine 300 has a catalyzed heat exchanger 180, which may be configuredas shown in FIG. 2 or may have other of the above-describedconfigurations. A fuel injector 185 provides hydrocarbon fuel for thesteam reformation.

Catalyzed Heat Exchanger with LPL EGR

FIG. 4 illustrates an engine 400 having a low pressure EGR loop andnon-dedicated EGR. In this EGR configuration, the “take-off” point forthe EGR loop 410 is from the main exhaust line 419, downstream ofturbine 404 b, but upstream aftertreatment device 420. In otherrespects, engine 400 is similar to engines 200 and 300.

Engine 400 has a catalyzed heat exchanger 180, which may be configuredas shown in FIG. 2 or may have other of the above-describedconfigurations. A fuel injector 185 provides hydrocarbon fuel for thesteam reformation.

Catalyzed Heat Exchanger Performance

FIG. 5 illustrates conversion of methane (CH₄) as a function oftemperature for both a membrane reactor (MR) and packed-bed reactor(PBR) as implementations of catalyst reactor 245. It is desired tomaintain exhaust temperatures as high as possible for effectiveproduction of H₂ and CO during the steam reforming process. Because thesteam reformation reaction is reversible in nature, continuous removalof H₂ from the gas feed (as is achieved with a membrane reactor) canresult in increased yields of H₂ and CO. Because the steam reformingreaction is highly endothermic (206 kJ/mol HC), thermal energy iscontinuously removed from the gas stream as hydrocarbon fuel isconverted to H₂ and CO. As described above, replacing thermal energythat is converted to chemical energy via transfer from the exhauststream can increase the yield of H₂ and CO from the steam reformingreaction.

It is expected that for exhaust temperatures within the catalyst of thecatalyzed heat exchanger 180 ranging between 773-923 degrees K,fractional conversion of methane can range from 0.4 to 0.9.

FIGS. 6 and 7 illustrate theoretical maximum H₂ and CO production,respectively, from catalyzed heat exchanger 180 as compared to othersteam reforming configurations. The solid line represents H₂ and COproduction with no heat exchanger, using only the thermal energy that isavailable in the EGR stream. The dashed line represents the use of anun-catalyzed heat exchanger and assumes doubling the thermal energyavailable in the EGR stream to drive the steam reforming reaction. Thedotted line represents the case of catalyzed heat exchanger 180, wherethe catalyst surface temperature is maintained at the same value as themain exhaust stream gas temperature. This is the optimal case, andclearly results in the highest theoretical conversion of H₂ and CO.

What is claimed is:
 1. A method of providing recirculated exhaust to aninternal combustion engine having a number of cylinders, the cylindersreceiving an intake charge via an intake line, with at least onecylinder being a dedicated EGR (exhaust gas recirculation) cylinder andthe remaining cylinders being main cylinders whose exhaust is emittedvia an exhaust manifold to a main exhaust line, comprising: providing anEGR loop to route recirculated exhaust from the dedicated EGR cylinderto a point on the intake line; installing a catalyzed heat exchanger onthe EGR loop; wherein the catalyzed heat exchanger has a catalystreactor and a heat exchanger; wherein the catalyst reactor is operableto perform a steam reformation process; installing a fuel injector onthe EGR loop upstream of the catalyzed heat exchanger; receiving ahydrocarbon fuel via the fuel injector into the EGR loop; receivingexhaust from the main exhaust line into the heat exchanger and using theexhaust from the main exhaust line to heat the catalyst reactor; andusing the catalyzed reactor to increase the amount of hydrogen andcarbon monoxide in the recirculated exhaust.
 2. The method of claim 1,wherein the hydrocarbon fuel is gasoline, diesel, methane, propane, orethanol.
 3. The method of claim 1, wherein the hydrocarbon fuel isdelivered from the same fuel reservoir as the used for the engine. 4.The method of claim 1, wherein the catalyst reactor is a membrane orpacked bed reactor.
 5. The method of claim 1, wherein the catalyst hascatalyst material comprising nickel, platinum, palladium, or rhodium. 6.The method of claim 1, wherein the engine has an exhaust aftertreatmentdevice, and the catalyzed heat exchanger receives exhaust downstream ofthe aftertreatment device.
 7. The method of claim 1, wherein the enginehas an exhaust aftertreatment device, and the catalyzed heat exchangerreceives exhaust upstream of the aftertreatment device.
 8. A method ofproviding recirculated exhaust to an internal combustion engine having anumber of cylinders, the cylinders receiving an intake charge via anintake line, and the cylinders emitting exhaust via a main exhaust line,comprising: providing an exhaust gas recirculation (EGR) loop to routerecirculated exhaust from at least one cylinder to a point on the intakeline; installing a catalyzed heat exchanger on the EGR loop; wherein thecatalyzed heat exchanger has a catalyst reactor and a heat exchanger;wherein the catalyst reactor is operable to perform a steam reformationprocess; installing a fuel injector on the EGR loop upstream of thecatalyzed heat exchanger; receiving a hydrocarbon fuel via the fuelinjector into the EGR loop; receiving exhaust from the main exhaust lineinto the heat exchanger and using the exhaust from the main exhaust lineto heat the catalyst reactor; and using the catalyzed reactor toincrease the amount of hydrogen and carbon monoxide in the recirculatedexhaust.
 9. The method of claim 8, wherein the EGR loop is a lowpressure EGR loop.
 10. The method of claim 8, wherein the EGR loop is ahigh pressure EGR loop.
 11. The method of claim 8, wherein the enginehas at least one cylinder that is a dedicated EGR cylinder and whereinthe EGR loop receives exhaust from the dedicated EGR cylinder.
 12. Themethod of claim 8, wherein the hydrocarbon fuel is gasoline, diesel,methane, propane, or ethanol.
 13. The method of claim 8, wherein thehydrocarbon fuel is delivered from the same fuel reservoir as the usedfor the engine.
 14. The method of claim 8, wherein the catalyst reactoris a membrane or packed bed reactor.
 15. The method of claim 8, whereinthe catalyst has catalyst material comprising nickel, platinum,palladium, or rhodium.
 16. The method of claim 8, wherein the engine hasan exhaust aftertreatment device, and the catalyzed heat exchangerreceives exhaust downstream of the aftertreatment device.
 17. The methodof claim 8, wherein the engine has an exhaust aftertreatment device, andthe catalyzed heat exchanger receives exhaust upstream of theaftertreatment device.